(607f) Highly Active Nanoporous Solid Base MgO Catalyst Derived from Mg-MOF-74 Towards Knoevenagel Reaction

Numerous potential applications of heterogenous base catalysts in a variety of industrial chemical processes indicates the urgent need of development of new strategies for fabrication of highly active solid base catalysts. Herein, we report the synthesis and application of a highly nanoporous magnesium oxide (MgO) derived from a Mg-based metal-organic framework (Mg-MOF-74) through thermal treatment under static air environment at 600 °C. In fact, the evaporation of the ligands, present in the structure of MOF-74 (i.e. 2,5-dihydroxyterephtalic acid), generates nanopores inside final structure of MgO, which play a key role in its enhancement activity towards catalytic reactions. The as-made nanoporous MgO exhibited high crystallinity and accurate structural phase formation as confirmed by XRD patterns in comparison with a conventional MgO fabricated from commercial Mg(NO₃)₂.6H₂O precursor (Fig.1). Moreover, according to the obtained results from temperature programmed desorption (TPD) analysis, the total number of active basic sites enhanced by six times in the MOF-derived MgO (595 µmol_CO2/g) compared to MgO commercial (96 µmol_CO2/g) whereas the nature of basic sites obtained from CO₂DRIFT (Fig.2) is the same. As it can be observed, the existence of absorbance bands at around 1680 and 1480 cm^-1, at 1320 and 1640 cm^-1, and also at 1520 to 1540 cm^-1 demonstrates the presence of low-strength, medium-strength, and high-strength basic sites, respectively.

Finally, the activity of produced nanoporous MgO was assessed in the Knoevenagel reaction carried out in a fixed-bed flow reactor under mild conditions (50 °C). The experimental results (Fig.3) unveiled significantly higher catalytic activity of the nanoporous MgO as it was confirmed by greater initial rate as well as smaller deactivation constants (K_d (1/h)).

Based on the presented results, MOF materials can be known as promising candidates for producing highly active nanoporous solid base catalysts that can be employed in various applications in industry.